Shape memory alloy actuator

ABSTRACT

An aircraft system may include an airfoil and a deployable device coupled to the airfoil. The system may further include a shape memory alloy actuator coupled between the airfoil and the deployable device. The actuator may be movable between a first position with the deployable device deployed relative to the airfoil, and a second position with the deployable device stowed relative to the airfoil. The system may additionally include an activatable link positioned between the actuator and the deployable device. The link may have an engaged configuration in which motion of the actuator is transmitted to the deployable device, and a disengaged configuration in which motion of the actuator is not transmitted to the deployable device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims priority topending application Ser. No. 10/771,489 entitled AIRCRAFT SYSTEMS WITHSHAPE MEMORY ALLOY (SMA) ACTUATORS AND ASSOCIATED METHODS filed on Jun.29, 2007, the entire contents of which is incorporated by referenceherein.

FIELD

The present disclosure is directed generally to aircraft systems withshape memory alloy (SMA) actuators, and associated methods.

BACKGROUND

Shape memory alloys (SMA) form a group of metals that have usefulthermal and mechanical properties. If an SMA material such as Nitinol isdeformed while in a martensitic state (low yield strength condition) andthen heated to its transition temperature to reach an austenitic state,the SMA material will resume its austenitic shape. The rate of return tothe austenitic shape depends upon the amount and rate of thermal energyapplied to the component.

SMA actuators have proven useful in a wide variety of contexts,including aircraft-related contexts, to actuate particular devices.However, the SMA actuators have, in at least some instances, provedchallenging to control. In other instances, the integration of SMAactuators has proved challenging. Accordingly, there exists a need inthe art for improved techniques for integrating SMA actuators intoaircraft systems, and controlling such actuators

SUMMARY

Aspects of the present disclosure are directed to aircraft systems withshape memory alloy (SMA) actuators, and associated methods. An aircraftsystem in accordance with a particular embodiment includes an airfoiland a deployable device coupled to the airfoil with a hinge. The hingehas a load path supporting the deployable device relative to theairfoil. The system can further include an SMA actuator coupled betweenthe airfoil and the deployable device, with the actuator being moveablealong a motion path different than the hinge load path between a firstposition with the deployable device deployed relative to the airfoil,and a second position with the deployable device stowed relative to theairfoil. In particular embodiments, the deployable device can include asecondary trailing edge device that depends from a primary trailing edgedevice. In further particular embodiments, the deployable device caninclude a noise-reduction hinge tab that deploys from a helicopterrotor.

In still another embodiment, the system can include an activatable linkpositioned between the actuator and the deployable device, with the linkhaving an engaged configuration in which motion of the actuator istransmitted to the deployable device, and a disengaged configuration inwhich motion of the actuator is not transmitted to the deployabledevice. For example, in a particular embodiment, the activatable linkincludes a clutch. In another embodiment, the activatable link includesa rotary spline having first spline elements and second spline elements,with the first and second elements rotatable relative to each other overa first angular range, and rotating together over a second rotationalrange.

Other aspects are directed to methods for operating an airfoil. Onemethod includes supporting a deployable device relative to an airfoilwith a hinge having a hinge load path, and moving the deployable devicerelative to the airfoil by activating an SMA actuator coupled betweenthe airfoil and the deployable device. Activating the actuator caninclude moving the actuator along a motion path different than the hingeload path. A method in accordance with another embodiment includes usinga selectively activatable link to engage an SMA actuator with thedeployable device and move the deployable device during a first mode ofoperation, and disengage the SMA actuator from the deployable deviceduring a second mode of operation, while the actuator is activated.

The features, functions and advantages that have been discussed can beachieved independently in various embodiments of the present disclosureor may be combined in yet other embodiments, further details of whichcan be seen with reference to the following description and drawingsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is partially schematic, isometric illustration of an overallsystem that includes an aircraft with one or more deployable devicesinstalled in accordance with an embodiment of the disclosure.

FIG. 2A is a partially schematic, bottom isometric illustration of adeployable device and an SMA actuator configured in accordance with anembodiment of the disclosure.

FIG. 2B is a partially schematic top isometric illustration of anembodiment of the arrangement shown in FIG. 2A, along with additionalcomponents.

FIG. 3 is a partially schematic, isometric illustration of a connectionarrangement between an SMA actuator and a deployable device inaccordance with an embodiment of the disclosure.

FIG. 4 is a partially schematic, cross-sectional illustration of anembodiment of the connection arrangement shown in FIG. 3.

FIG. 5 is a partially schematic, plan view illustration of an SMAactuator coupled to a deployable device with an activatable link inaccordance with an embodiment of the disclosure.

FIG. 6 is a partially schematic, side elevation view of a deployabledevice coupled to an SMA actuator with a rack and pinion arrangement inaccordance with another embodiment of the disclosure.

FIG. 7 is a top isometric illustration of a rotor blade that includesmultiple deployable devices in accordance with an embodiment of thedisclosure.

FIG. 8 is a partially schematic, isometric illustration of thedeployable devices shown in FIG. 7.

FIG. 9 is a partially schematic, isometric illustration of an SMAactuator and associated connections with the deployable devices shown inFIG. 8.

FIGS. 10A-10D illustrate phases of operation of the actuator arrangementshown in FIGS. 7-9.

DETAILED DESCRIPTION

The following disclosure is directed generally toward aircraft systemswith shape memory alloy (SMA) actuators, and associated methods. Severaldetails describing structures and/or processes that are well-known andoften associated with aspects of the systems and methods are not setforth in the following description for purposes of brevity. Moreover,although the following disclosure sets forth several embodiments ofrepresentative aspects of the disclosure, several other embodiments canhave different configurations or different components than thosedescribed in this section. For example, other embodiments may haveadditional elements and/or may delete several of the elements describedbelow with reference to FIGS. 1-10D.

FIG. 1 illustrates an aircraft 105 that can form a portion of an overallaircraft system 100. The aircraft 105 includes a fuselage 101, wings110, horizontal stabilizers 102, and a vertical stabilizer 103. Any ofthese components can include deployable devices, but for purposes ofillustration, selected deployable devices are described further below inthe context of trailing edge devices mounted to the wings 110. The wings110 can each include a leading edge 111, a trailing edge 112, and one ormore trailing edge devices 118 (e.g., flaps 113, ailerons, or flaperons)carried at the trailing edge 112. The trailing edge devices 118, whichare themselves deployable relative to the wing 110, can include furtherdeployable devices that are driven by SMA actuators, as described infurther detail below. For purposes of illustration, the followingdiscussion is provided in the context of a trailing edge flap 113. Inother embodiments, some or all aspects of the components described belowcan be applied to other trailing edge devices 118, and/or othernon-trailing edge devices.

FIG. 2A is a bottom isometric illustration of the aft portion of one ofthe trailing edge flaps 113 shown in FIG. 1. For purposes ofillustration, portions of the external skin of the trailing edge flap113 are removed. The trailing edge flap 113 includes a deployable device120 (e.g., a “mini” or other secondary trailing edge device) that iscarried toward the aft edge of the trailing edge flap 113. The trailingedge flap 113 accordingly includes a deployable device receptacle 115that receives the deployable device 120 in a stowed position. An SMAactuator 122 is coupled to the deployable device 120 to move it betweenits deployed position (shown in FIG. 2) and its stowed position.Accordingly, the SMA actuator 122 can be connected between one or moreflap brackets 114 carried by the trailing edge flap 113, and one or moredevice brackets 121 carried by the deployable device 120.

FIG. 2B is a top isometric illustration of the arrangement shown in FIG.2A, along with additional components. These components can includereturn springs 135 (shown schematically) that bias the deployable device120 toward either the stowed or deployed position (generally the stowedposition). The arrangement can also include one or more thermoelectricmodules 143 coupled to the SMA actuator 122 with thermally conductivecouplings 144 (e.g., copper straps) to cool the actuator 122. One ormore position sensors 145 can be used for diagnostic purposes toidentify the position of the deployable device 120.

FIG. 3 is a partially schematic illustration of the aft portion of thetrailing edge flap 113, and the forward portion of the deployable device120. As shown in FIG. 3, a hinge pin 123 passes through, and isrotatable relative to, a plurality of flap brackets 114. The hinge pin123 can be fixedly clamped to the device brackets 121. Accordingly, thehinge pin 123 can rotate with the deployable device 120, and rotaterelative to the trailing edge flap 113. In other embodiments, thisarrangement can be reversed. In any of these embodiments, the SMAactuator 122 can be carried within an axially extending opening of thehinge pin 123 to drive the deployable device 120 relative to thetrailing edge flap 113. Further details of a representative embodimentfor arranging the SMA actuator 122 and the hinge pin 123 are describedbelow with reference to FIG. 4.

FIG. 4 is a partially schematic, top cross-sectional illustration ofembodiments of the system portions shown in FIG. 3. As shown in FIG. 4,the hinge pin 123 is fixedly attached to the device brackets 121, and isrotatable within apertures of the flap brackets 114. For purposes ofillustration, bearings (e.g., ball bearings) and/or other features thatsupport the relative rotation of the hinge pin 123 are not shown in FIG.4. The SMA actuator 122 is received in an annular channel 146 of thehinge pin 123 and is attached at one end to an actuator support 125. Theopposite end of the SMA actuator 122 is attached to the hinge pin 123,e.g., at an actuator/hinge pin connection 124. When the SMA actuator 122is heated (e.g., by applying an electrical current to the actuator 122),it tends to twist, as indicated by arrow A. Because one end of the SMAactuator 122 is fixed relative to the trailing edge flap 113, thetwisting motion of the SMA actuator 122 rotates the hinge pin 123relative to the trailing edge flap 113. This motion in turn rotates thedeployable device 120 relative to the trailing edge flap 113, asindicated by arrow D. In a particular arrangement, the deployable device120 is in its stowed position when the SMA actuator 122 is inactive(e.g., cooled), and rotates to its deployed position when the SMAactuator is activated (e.g., heated). In other embodiments, the SMAactuator 122 can be configured in the opposite sense.

In any of the foregoing embodiments described above with reference toFIGS. 3 and 4, the deployable device 120 can be carried and supportedrelative to the trailing edge flap 113 via a hinge load path, and thedeployable device 120 can be moved relative to the trailing edge flap113 along a motion path that is different, at least in part, than theload path. For example, as shown in FIG. 4, the load path supporting thedeployable device 120 relative to the trailing edge flap 113 includesthe device brackets 121, the hinge pin 123, and the flap brackets 114.The motion path between the deployable device 120 and the trailing edgeflap includes the device brackets 121, the hinge pin 123, the SMAactuator 122, and the actuator support 125. An advantage of thisarrangement is that the deployable device 120 will remain attached tothe trailing edge flap 113, even in the unlikely event of a completefailure of the SMA actuator 122. For example, if the SMA actuator 122were to fracture in such a way that it no longer provides mechanicalcontinuity between the actuator support 125 and the hinge pin 123, theflap brackets 114 still provide a continuous load path between thedeployable device 120 and the trailing edge flap 113. The load pathprovided by the flap brackets 114 can accordingly provide a fail-safeconnection between the trailing edge flap 113 and the deployable device120.

One characteristic of SMA actuators that has proved challenging todesigners is the fact that many SMA actuators have different responsecharacteristics over different portions of their actuation ranges. Forexample, typical SMA actuators may move relatively slowly at thebeginning of the actuation range, move more quickly in the middle of therange, and then slow down again toward the end of the range. Anothercharacteristic of many SMA actuators is that, once activated, theyrequire power to remain in their actuated positions. Particularembodiments of systems that address both of these challenges aredescribed below.

FIG. 5 is a partially schematic, partial cross-sectional top plan viewof the deployable device 120 coupled to the trailing edge flap 113 withone or more activatable links 526 configured in accordance with anembodiment of the disclosure. In this embodiment, two SMA actuators 522are coupled between the trailing edge flap 113 and the deployable device120. In one particular embodiment, each SMA actuator 522 rotates in thesame direction when actuated, and accordingly, the two SMA actuators 522can provide a redundant actuation capability. In other embodiments, eachof the SMA actuators 522 can rotate the deployable device 120 inopposite directions. Accordingly, one SMA actuator 522 can be used todeploy the deployable device 120, and the other can be used to stow thedeployable device 120. In either of these arrangements, the SMAactuators 522 are connected to an actuator support 525 that is fixedrelative to the trailing edge flap 113. The motion of the SMA actuators522 is then selectively transmitted to the deployable device 120 via twocorresponding activatable links 526. In a first mode of operation, theactivatable links 526 transmit motion of the actuators 522 to thedeployable device 120, and in a second mode of operation, they do not,as described further below.

Each activatable link 526 can include a pin 523 connected at one end toa solenoid 527, and at the other end to a clutch 528 that selectivelyengages with the neighboring SMA actuator 522. Pin bearings 530 supportthe pin 523, and actuator bearings 531 support the SMA actuator 522. Ina particular embodiment, the pin 523 is slidable relative to the devicebracket 122 through which it passes, but is not rotatable relative tothe device bracket 121. For example, the hinge pin 523 can includesplines that are slideably received in a corresponding opening in thedevice bracket 121. When the clutch 528 is disengaged (as shown in FIG.5), the motion of each SMA actuator 522 is not transmitted to thedeployable device 520. When the solenoid 527 is activated, the clutch528 engages, and the motion of the SMA actuator 522 is transmitted tothe deployable device 120. In this manner, the clutch 528 can bedisengaged while the SMA actuator 522 is moving slowly (e.g., toward thestart and/or end of its motion range), and can be engaged when the SMAactuator is moving more quickly (e.g., in the middle of its motionrange). A controller 542 can automatically control the solenoids 527(and therefore the state of the corresponding clutches 528) to takeadvantage of the quickest portion of the actuator motion range.

The controller 542 can also be coupled to a lock 529 that selectivelyengages the deployable device 120, or a component fixedly attached tothe deployable device 120 (e.g., the device bracket 121). Accordingly,the SMA actuators 522 can be used to drive the deployable device 120 toits deployed position, and then the lock 529 can engage the deployabledevice 120 and prevent (or at least restrict or inhibit) it fromreturning to its stowed position. The controller 542 can thendiscontinue power to the SMA actuators 522, allowing the SMA actuators522 to return to their “relaxed” state, which does not require power.When the deployable device 120 is to be returned to its stowed position,the lock 529 can be disengaged and the SMA actuators 522 and/or a springdevice (e.g., the return springs 135 shown in FIG. 2B) can return thedeployable device 120 to its stowed position. Further details of arepresentative arrangement for executing these processes are describedwith reference to FIGS. 10A-10D.

FIG. 6 illustrates a deployable device 120 driven by an SMA actuator 622in accordance with another embodiment of the disclosure. In one aspectof this embodiment, the deployable device 120 is carried by a trailingedge flap 113 having a flap lower surface 616 with a gap 615 throughwhich the deployable device 120 emerges when deployed. The deployabledevice 120 has a guide pin 634 that moves along a guide track 617carried by the trailing edge flap 113, forming a sliding hingearrangement. The deployable device 120 also includes a rack 632 thatengages with a pinion 633 carried by the trailing edge flap 113. Aroller or other device (not shown in FIG. 6) can apply a force to thedeployable device 120 to keep it engaged with the pinion 633. In anotherembodiment, the pinion 633 is positioned below the deployable device120, and gravity provides the force described above. In any of theseembodiments, the pinion 633 can be connected to, and rotated by, the SMAactuator 622. Accordingly, when the SMA actuator 622 is activated, itrotates the pinion 633, which in turn moves the deployable device 120into and out of the receptacle 615 by engaging with and driving the rack632. Any of the foregoing arrangements for selectively actuating the SMAactuator 622 and/or locking the SMA actuator 622 can be included in thearrangement shown in FIG. 6. In the unlikely event that the SMA actuator622 fails, the deployable device 120 can remain secured to the trailingedge flap because the guide pin 634 remains engaged with the guide track617.

SMA actuator arrangements having characteristics similar at least inpart to the embodiments described above can be coupled to other types ofairfoils, and/or can have different arrangements in other embodiments.For example, FIGS. 7-10D illustrate portions of a rotor blade 710 havingdeployable devices 720 arranged in accordance with one such embodiment.Beginning with FIG. 7, the rotor blade 710 can include two deployabledevices 720, e.g., a first deployable device 720 a which is visible inFIG. 7, and a second deployable device 720 b described below withreference to FIG. 8. The deployable devices 720 can be deployed from therotor blade 710 to reduce rotor noise, for example, during hoveroperations in environments having stringent noise attenuationrequirements. The deployable devices 720 can be operated with rotary SMAactuators, as is described further below.

FIG. 8 is a partially schematic, isometric illustration of the first andsecond deployable devices 720 a, 720 b and associated hardware, removedfrom the rotor blade 710 shown in FIG. 7. The deployable devices 720 a,720 b are supported relative to the rotor blade 710 with blade brackets714. Return springs 735 can return the deployable devices 720 a, 720 bto their stowed positions without the need for simultaneously activatinga corresponding SMA actuator, as is described further below.

FIG. 9 is another isometric view of the arrangement shown in FIG. 8,with the first deployable device 720 a removed to expose internalfeatures of the arrangement. The arrangement includes a single SMAactuator 722 that is free to rotate with respect to the blade brackets714. The SMA actuator 722 is coupled toward opposing ends tocorresponding drivers 736 (including a first driver 736 a that isvisible in FIG. 9 and a second driver 736 b that is not visible in FIG.9). A connector shaft 737 provides the connection between the SMAactuator 722 and the drivers 736 a, 736 b. The connector shaft 737 alsoextends through the blade brackets 714 so that if the SMA actuator 722fails, the corresponding deployable device is still carried in positionrelative to the rotor blade 710 (FIG. 7).

In a particular embodiment, each driver 736 includes a spline 738 havingat least one first spline element 739 that selectively engages with acorresponding spline element carried by one of the deployable devices720 a, 720 b. As the SMA actuator 722 twists about its longitudinalaxis, the first and second drivers 736 a, 736 b rotate in oppositedirections. During at least a portion of this relative movement, thedrivers 736 a, 736 b move the corresponding deployable devices 720 a,720 b in opposite directions. The motion of the two devices 720 a, 720 bis coordinated by a motion coordinator 750. In a particular embodiment,the motion coordinator 750 can include first and second opposingcoordination arms 751 a, 751 b, each of which is carried by acorresponding one of the deployable devices 720 a, 720 b (e.g., thesecond coordination arm 751 b is carried by the second deployable device720 b). Each coordination arm 751 a, 751 b includes a rack 752 thatengages with a centrally located pinion 753. When one of the deployabledevice, 720 a, 720 b moves, the pinion 753 transmits the motion to otherdeployable device 720 a, 720 b so as to move the other deployable deviceby the same amount in the opposite direction.

FIGS. 10A-10D are partially schematic, cross-sectional illustrations ofthe rotor 710, showing the SMA actuator 722 and the second driver 736 bof FIG. 9A during various phases of operation. As shown in FIG. 10A, thesecond driver 736 b includes a spline 738 having a first spline element739. As the SMA actuator 722 twists, the first spline element 739rotates as indicated by arrow A until it engages a corresponding secondspline element 740 carried by the second deployable device 720 b (FIG.10B). If the first driver 736 a (FIG. 9) has not yet engaged with acorresponding second spline element carried by the first deployabledevice 720 a (FIG. 9), then in a particular embodiment, the SMA actuator722 continues to twist without further rotating the second driver 736 b.When, for both the first and second drivers 736 a, 736 b, the firstspline element 739 engages the corresponding second spline element 740(as shown in FIG. 10C), continued twisting by the SMA actuator 722causes the first deployable device 720 a and the second deployabledevice 720 b to rotate away from each other, as indicated by arrows D.This motion is coordinated by the motion coordinator 750 described abovewith reference to FIG. 9.

At the end of the relative motion between the first and seconddeployable devices 720 a, 720 b, a lock 729 can deploy a lock element741, as indicated by arrow L₁, to hold the deployable devices 720 a, 720b in their deployed positions or at least inhibit motion of thedeployable devices 720 a, 720 b. With the lock element 741 in this firstor locked position, the SMA actuator 722 can unwind or relax, asindicated by arrow R in FIG. 10D. At the same time, the deployed lockelement 741 can maintain the first and second deployable devices 720 a,720 b in their deployed positions. When it is desired to retract thedeployable devices 720 a, 720 b, the lock element 741 can retract to asecond or unlocked position, as indicated by arrow L₂ in FIG. 10D. Thereturn springs 735 (one of which is visible in FIG. 10D) can then returnthe deployable devices 720 a, 720 b to the configuration shown in FIG.10A.

One feature of several of the foregoing embodiments is that the motionpath and load path between the deployable device and the structure fromwhich it depends are separate. An advantage of this arrangement is thatthe SMA actuator can fail, without causing the deployable device toseparate from the structure that carries it. In a particulararrangement, the SMA actuator can be housed, at least in part, in anaxial channel of a hinge pin that connects the deployable device to anassociated support structure. This configuration can provide the addedadvantage of a nested, compact arrangement.

Another feature of at least some of the foregoing embodiments is thatthe SMA actuator can be selectively coupled to and decoupled from thedeployable device, for example, with a clutch, a selectively engagedspline, or other arrangement. An advantage of these arrangements is thatthe deployable device can be selectively coupled to the SMA actuatorduring particular motion phases of the SMA actuator. For example, thedeployable devices can be coupled to the SMA actuators only during thoseportions of the SMA actuator's motion that are at or above a selectedthreshold speed. This arrangement can avoid low speed deployment orretraction of the deployed devices.

Still another feature of at least some of the foregoing embodiments isthat they can include a selectively deployable lock that keeps thedeployed device in a particular position (e.g., a stowed position) evenif the SMA actuator is unpowered. This arrangement can reduce the amountof power consumed by the SMA actuator. It can also reduce the timerequired to reposition the deployed device. For example, when thedeployed device is provided with a return spring or other returnmechanism, it can move to the stowed position more quickly than if thereturn motion were controlled by the cooling rate of the SMA actuator.

Representative materials suitable for manufacturing SMA actuators inaccordance with any of the embodiments described above include Nitinol.In a particular embodiment, the Nitinol can be 55% by weight nickel and45% by weight titanium. In a further particular embodiment, the Nitinolcan have an equi-atomic composition, with 50% nickel molecules and 50%titanium molecules. Suitable materials are available from Special MetalsCorp. of New Hartford, N.Y., and Wah Chang of Albany, Oreg. The materialis then machined, heat treated and trained. The resulting structure candisplay shape memory effects, including a two-way shape memory effect.Further details of suitable manufacturing processes and resultingstructures are included in pending U.S. Application PublicationUS2005-0198777, assigned to the assignee of the present application andincorporated herein by reference. Other suitable materials includeNitinol with 57% or 60% nickel by weight, and/or nickel/titanium alloyswith additional constituents (e.g., palladium and/or platinum) toincrease the transition temperature, and/or to attain other materialproperties.

From the foregoing, it will be appreciated that specific embodimentshave been described herein for purposes of illustration, but thatvarious modifications may be made in other embodiments. For example, theSMA actuators and couplings described above can have other features andarrangements in other embodiments. The SMA actuators can be used todrive devices other than the mini trailing edge devices and rotor tabsdescribed above, including other secondary trailing edge devices thatare attached to a primary trailing edge device (e.g., a double-slottedtrailing edge device). In still further embodiments, the SMA actuatorscan have an actuation motion path other than the rotary or twistingmotion path described above (e.g., a linear motion path).

Certain aspects described in the context of particular embodiments maybe combined or eliminated in other embodiments. For example, the lockarrangement described above with reference to FIGS. 7-10D can bemodified and incorporated into the device shown in FIG. 5. Further,while advantages associated with certain embodiments have been describedin the context of those embodiments, other embodiments may also exhibitsuch advantages, and not all embodiments need necessarily exhibit suchadvantages. Accordingly, embodiments of the disclosure are not limitedexcept as by the appended claims.

What is claimed is:
 1. An aircraft system, comprising: an airfoil; a deployable device coupled to the airfoil; a shape memory alloy actuator coupled between the airfoil and the deployable device, the actuator being movable between a first position with the deployable device deployed relative to the airfoil, and a second position with the deployable device stowed relative to the airfoil; and an activatable link positioned between the actuator and the deployable device, the link having an engaged configuration in which motion of the actuator is transmitted to the deployable device, and a disengaged configuration in which motion of the actuator is not transmitted to the deployable device.
 2. The system of claim 1 wherein: the actuator is movable along a rotary motion path.
 3. The system of claim 2 wherein: the actuator is twistable relative to at least one of the airfoil and the deployable device along the rotary motion path.
 4. The system of claim 3 further comprising: a hinge coupled between the airfoil and the deployable device; the hinge including a hinge pin having an elongated opening; the shape memory alloy actuator being positioned within the opening to twist along the motion path.
 5. The system of claim 4 wherein: the shape memory alloy actuator having a first end fixed to the hinge pin and a second end fixed to the airfoil.
 6. The system of claim 1 further comprising: a hinge coupled between the airfoil and the deployable device, the hinge defining a hinge load path supporting the deployable device relative to the airfoil.
 7. The system of claim 1 wherein: the actuator has a range of motion; the activatable link coupling the actuator to the deployable device over a first portion of the range of motion and not over a second portion of the range of motion.
 8. The system of claim 1 wherein: the activatable link includes a rotary spline having first spline elements and second spline elements; the first and second spline elements being disengaged and rotatable relative to each other over a first angular range; the first and second spline elements being engaged and rotatable together over a second rotational range.
 9. The system of claim 1 further comprising: an activatable lock coupled between the deployable device and the airfoil; the lock having a locked configuration in which the deployable device has a fixed position relative to the airfoil, and an unlocked configuration in which the deployable device is movable relative to the airfoil.
 10. The system of claim 1 wherein: the airfoil comprises a wing of an aircraft; the deployable device comprises at least one of a trailing edge device coupled to the wing.
 11. An aircraft system, comprising: an airfoil; a trailing edge device coupled to the airfoil; a shape memory alloy actuator coupled between the airfoil and the trailing edge device, the actuator being movable between a first position with the trailing edge device deployed relative to the airfoil, and a second position with the trailing edge device stowed relative to the airfoil; and an activatable link positioned between the actuator and the trailing edge device, the link having an engaged configuration in which motion of the actuator is transmitted to the trailing edge device, and a disengaged configuration in which motion of the actuator is not transmitted to the trailing edge device.
 12. A method for deploying a deployable device, comprising the steps of: supporting the deployable device relative to an airfoil; activating a shape memory alloy actuator coupled between the airfoil and the deployable device; twisting the shape memory alloy actuator along a rotary motion path; and moving the deployable device relative to the airfoil in response to twisting the shape memory alloy actuator.
 13. The method of claim 12 wherein the step of twisting the actuator comprises: twisting the actuator relative to at least one of the airfoil and the deployable device.
 14. The method of claim 13 wherein the step of twisting the actuator comprises: heating the actuator; and twisting the actuator in response to the heating thereof.
 15. The method of claim 12 wherein the deployable device is supported on the airfoil by a hinge defining a hinge load path, the method further comprising the step of: moving the actuator along a motion path that is different than the hinge load path.
 16. A method for deploying a deployable device, comprising the steps of: supporting the deployable device relative to an airfoil; activating a shape memory alloy actuator coupled between the airfoil and the deployable device; moving the deployable device relative to the airfoil in response to activating the shape memory alloy actuator; engaging the shape memory alloy actuator with the deployable device to move the deployable device during a first mode of operation; and disengaging the shape memory alloy actuator from the deployable device during a second mode of operation.
 17. The method of claim 16 wherein the steps of engaging and disengaging the actuator with the deployable device during respective first and second modes of operation comprise: disengaging the actuator from the deployable device over a first range of motion of the actuator; and engaging the actuator with the deployable device over a second range of motion of the actuator.
 18. The method of claim 16 wherein the steps of engaging and disengaging the actuator with the deployable device during respective first and second modes of operation comprise: engaging the actuator while the actuator moves at a first speed; and disengaging the actuator while the actuator moves at a second speed.
 19. The method of claim 12 further comprising the steps of: locking the deployable device in a deployed position; allowing the shape memory alloy actuator to return to a relaxed state when the deployable device is in the deployed position.
 20. The method of claim 19 further comprising the steps of: unlocking the deployable device from the deployed position; returning the deployable device to a stowed positioned using a return mechanism. 